1. Field of the Invention
This invention relates to a power transmitting device, more particularly, a power transmitting device in which maximal output speed is produced by a planetary transmission and a overdrive which is driven by a power source unit.
2. Prior Art
A conventional power transmitting device employs a plurality of for improving performance of drive power which is generated by a power source.
In general the power is transmitted by the transmitting device for output at optimal speed and torque. It is important to adapt the transmission for the optimal speed and torque.
An example of the transmitting device is a transmission which includes an assembled gearset with a differential gear ratio respectively; the transmission outputs the speed according to a drive power which is output from the power source.
Presently transmissions are manual and automatic transmissions. The automatic transmission objective is to provide output at optimal speed and improve fuel efficiency.
Various attempts have been made to increase the speed ratio produced by the automatic transmission by adding an auxiliary gearset which operates via an initial planetary gearset, multiple gearset, and a last gearset.
The auxiliary gearset is coaxially aligned with an input shaft or a crankshaft of the power source.
An example of such device is disclosed in U.S. Pat. No. 5,538,482, of Tanzer et al. issued on Jul. 23, 1996 which describes a multiple-speed axle mechanism providing overdrive and direct drive. Tanzer increases the speed ratio by using a clutch having first friction elements and a brake means. Thus it can operate in an overdrive mode. Such device has a clutch and brakes adapted to two main axles respectively, so it has a complex structure and only operates in a single overdrive mode.
Another example of the overdrive device is disclosed in U.S. Pat. No. 5,951,424, of Briceland issued on Sep. 14, 1999. Briceland discloses a continuous variable drive transmission. Briceland claims only a simple planetary gearset like the conventional overdrive device. However, it is unsatisfactory because the increase of speed ratio is only 25% which has limited_cl=0 by the formula of Briceland.
Another multiple speed automotive transmission is disclosed in U.S. Pat. No. 5,868,645, of Beim et al. issued on Feb. 9, 1999. Beim discloses a variable multiple speed transmission. Many shafts which driven by a power source, e.g. intermediate shaft, input shaft and output shaft, result in a loss of torque during transmission between the shafts. To regain torque loss of the shafts, a drive clutch is installed. However, this is a conventional manually-operated transmission.
The above disclosures are attempts to improve fuel economy with the transmission and overdriver respectively, which have no reference to the auxiliary device.